In a blender, puree the chopped onion and the garlic with the garam masala or curry powder, 1/2 cup of the yogurt, 1/4 cup of the vinegar, 1/2 teaspoon salt, and 1/4 teaspoon pepper.,Transfer to a medium bowl, add the chicken, and turn to coat.,Let marinate in the refrigerator for at least 1 hour, or up to 1 day.,Heat 1 tablespoon of the oil in a large nonstick skillet over medium heat.,Shake the excess marinade off the chicken.,Cook the chicken until browned and cooked through, 6 to 7 minutes per side.,Let rest for 5 minutes before slicing.,Meanwhile, in a large bowl, whisk together the remaining 1/4 cup of yogurt, 2 tablespoons of vinegar, and 1 tablespoon of oil with 1 tablespoon water, 1/2 teaspoon salt, and 1/4 teaspoon pepper.,Add the lettuce, chickpeas, and sliced onion and toss to combine.,______